Warming drives dissolved organic carbon export from pristine alpine soils

Despite decades of research, the influence of climate on the export of dissolved organic carbon (DOC) from soil remains poorly constrained, adding uncertainty to global carbon models. The limited temporal range of contemporary monitoring data, ongoing climate reorganisation and confounding anthropogenic activities muddy the waters further. Here, we reconstruct DOC leaching over the last ~14,000 years using alpine environmental archives (two speleothems and one lake sediment core) across 4° of latitude from Te Waipounamu/South Island of Aotearoa New Zealand. We selected broadly comparable palaeoenvironmental archives in mountainous catchments, free of anthropogenically-induced landscape changes prior to ~1200 C.E. We show that warmer temperatures resulted in increased allochthonous DOC export through the Holocene, most notably during the Holocene Climatic Optimum (HCO), which was some 1.5–2.5 °C warmer than the late pre-industrial period—then decreased during the cooler mid-Holocene. We propose that temperature exerted the key control on the observed doubling to tripling of soil DOC export during the HCO, presumably via temperature-mediated changes in vegetative soil C inputs and microbial degradation rates. Future warming may accelerate DOC export from mountainous catchments, with implications for the global carbon cycle and water quality.


REVIEWER COMMENTS
Reviewer #1 (Remarks to the Author): Pearson and co-authors present a study on reconstrucfing DOC export from soils, using speleothems and a lake sediment core from Aotearoa New Zealand.The results are clearly novel and address an important quesfion, as soil DOC export and its response to global warming are poorly constrained and understudied.This is parficularly due to a lack of possibilifies to invesfigate the lability of DOC to warming in absence of anthropogenic interferences.Thus, the development of a method and archives that allow us to go further back in fime and study soil DOC export during past periods of warming without human influence is important and fimely.
While I think this study is well thought through and the methods seem valid and solidly carried out, I have some major concerns with the interpretafion of the results, which often seem overconfident and not backed up enough by the data.At this point, I don't see the data in the study allowing the conclusions merifing publicafion in Nature Communicafions.However, I have some suggesfions for improvement that may be addressed during a revision and may lead to clarificafion and more robust interpretafions.
1) The DOC concentrafion proxy from speleothems and lake records has been developed and calibrated in previous studies, parficularly Pearson et al., 2020.I commend the authors for their terrific work with the proxy development and validafion.However, I would like to see some more crifical assessment of the uncertainfies that affect the DOC proxy.For example, while the humic-like fluorescence component can be separated from other components such as protein-like, and therefore the soil-derived signal can be isolated from e.g., microbial components, I assume there is no way to isolate a signature that could come from soil-derived OM previously exported at depths below the soil?If such a component of OM existed and was periodically exported as DOC, could it lead to an over-esfimafion of the soil DOC export at these fimes?What about the general uncertainfies with the interpretafion of fluorescence signals and the calibrafion to DOC amounts?What about uncertainty in the meaning of the humic-like component (i.e., does it always have to relate to soil OM or are there other potenfial sources?).I really would welcome a more nuanced discussion of this proxy and the reliability of the results (parficularly in terms of quanfitafive reconstrucfion) in the paper, since as it stands it seems overconfident and potenfially misleading.
2) The interpretafion of speleothem Mg/Ca as a tracer for effecfive precipitafion is not well backed up by data or further references.While Mg/Ca can be a tracer for effecfive infiltrafion, it can also relate to other processes, such as water-rock interacfion (variability in the host rock composifion).Is there monitoring data from the two caves that can help determining if this is the case?Data from the host rock?Replicafion with other speleothems?In any case, the authors need to provide more background informafion on how the interpretafion of Mg/Ca was derived.It would also be nice to see a comparison with modelling data, as a check whether their hydroclimafic interpretafion reflects modelled condifions (check Scheff et al., 2017, Journal of Climate for a nice example).Moreover, it is unclear to me whether the results shown are based off one single laser ablafion track?This could also lead to strong skewing of the results, based on lateral variability of Mg/Ca in the stalagmite.Without long-term monitoring and more detailed analysis of the flowstones (e.g., more than one LA sampling track) this is a rather tenuous interpretafion.In that case, the claim that warming is the dominant driver of DOC export from these soils, and not hydroclimate, would not be backed up by the data.Similarly, the interpretafion of possible seasonality signals in the data seems mostly based off of speculafion.A clearer descripfion of how the data was generated and what gives the authors confidence that this proxy reflects effecfive precipitafion at both cave sites is needed, including reflecfion on what potenfial sources of uncertainty could be, and how they would affect the results.
3) In general, the interpretafion often lacks specificity and the data to back up some of the claims appears insufficient.Some of the claims seem cherry picked, and often are based on 1-2 data points given the resolufion of the records.I tried poinfing them out in the list of line-by-line comments below.Again, toning down the language in the manuscript, providing more details as to what could be potenfial complexifies or issues in the dataset, would lead to a much more interesfing and robust paper.line 188 and following: I find the separafion of the three periods a bit confusing.Here, the peak described seems to already be in stage 2 at about 12ka? (Difficult to be sure because of the axis being in z-score and text in absolute numbers).Either way, it seems to me that the Hodge creek cave record also mainly oscillates.There is a very high DOC value at 12 ka, but then values decrease again to levels comparable to the glacial and close to the mean of today.So the wording here is misleading.line 194: Why is there only Mg/Ca in Dave's cave for this period?The speleothem at Hodge Creek cave appears to have been growing at that fime?line 224: is this short interval of very high DOC samples based on a single sample?Does the average of the HCO include this peak?What if this is an outlier, how would the values of the HCO without it compare to today?line 232-234: Could the appearance of trees later in the record hint towards trees retaining more DOC, for example by reducing soil erosion?It would be nice if the authors could elaborate on whether, rather than only temperatures, the ecosystem change would affect DOC export.line 369: Could the handling of the sample, embedding in resin and EtOH wash affect the fluorescence signal?

Reviewer comments: Warming increases dissolved organic carbon export from prisfine alpine soils
There is plenty of novelty in this manuscript, where the authors present records of organic carbon fluxes over the last ~14,000 years from duplicated speleothems and a lake sediment core.This is the first such speleothem-based reconstrucfion, and the evidence is of higher organic carbon fluxes at these alpine sites in the early Holocene, declining to the present day.
The authors propose a direct link with warming through comparison with sea surface temperature reconstrucfions for the region.However, there was also vegetafion change over fime as discussed in the manuscript.And also, soil formafion and soil stability will change over fime (e.g.Retallack, 2021), as the region recovered from the last glaciafion.For this reviewer, these two alternate hypotheses (H: that the change in DOC export is due to changes in OC supply due to vegetafion change; H: that the change in DOC export is due to soil formafion and soil stability changes over fime) need to be tested and refuted for the case to be made that the DOC export trends are due to temperature alone.Some evidence is presented for vegetafion change, with evidence for the tree line changing over fime and it seems that land cover and vegetafion change would have occurred at the sites.Would addifional trace element profiles using LA-ICP-MS help provide addifional informafion on soil stability?I would add that in my opinion, the novelty of using speleothem and lake archives to reconstruct DOC over fime is huge, irrespecfive of whether it is temperature, vegetafion change, soil formafion or something else.
A major novelty here is the use of speleothems to derive a proxy record of DOC.The approach, using fluorescence EEMs on dissolved powders, builds on Pearson et al (2020), and here uses a calibrafion against deep peat water extracts to quanfify DOC in the speleothems in the past.Because of the novelty of the method, I would recommend that the calibrafion curve is provided in the Supplemental for the reader to assess.Also, the speleothem EEMs from the PARAFAC model are not shown, yet the endmembers are.Again, it would be good to see this in the supplemental, so that the reader can see how alike the proxy EEMs are similar to the peat extracts end members.
The authors use a parficular type of speleothem -flowstone -which is deposited at the base of flowing water.Flowstones are rarely used for paleoclimate research -stalagmites are favoured as their strafigraphy is simpler and their hydrology relafively constrained (at least to water dripping onto their surface).The use of flowstone becomes relevant when the use of Mg/Ca rafios is introduced on Line 170.The authors state that this is a rainfall proxy, but this has to be demonstrated.As stated by the authors, it is a proxy for the fime the water has previously had to precipitate calcite.For a flowstone, this could be along the flow path in the cave, and weakly or unrelated to rainfall.The authors provide duplicate flowstones, which show a lack of agreement in Mg/Ca over fime in the early part of the records of the two samples.This suggests that it is not a direct rainfall proxy, and instead there is a karst hydrology control on the water evolufion and flow paths for these two flowstones.This is important as the reconstructed DOC records are fluxes (e.g.mg/L) and it seems this is a combinafion of both source (supply) and flux (dilufion).Again, the use of flowstones might be disadvantageous here, as they likely have higher water flux variability compared to stalagmites.
As far as I could tell, the authors do not consider or quanfify the possible contribufion of OC in the speleothems from the in-cave microbial community that will be present on the flowstone surface.This might be a small contribufion relafive to the soil, but should be addressed.If the PARAFAC components are presented, the reader would be able to assess whether there is a microbial component.This is parficularly important as I beleive Pearson et al (2020) previously suggested there is a microbial OM fluorescence signal in a NZ flowstone.It would be useful to understand more about any in-cave contribufion to the speleothem record, how it changes over fime and between samples, and whether it also co-relates with the other PARAFAC and environmental parameters.On the whole, I like this paper.It tackles an important research quesfion (drivers of aquafic DOC dynamics).It also takes a long term perspecfive (Holocene durafion) compared to most other studies on this topic which consider monitoring records which are only of decades durafion.There is also a good overall finding that the speleothem DOC record can be broadly corelated with records of sea surface temperature, thus lending impact to the paper.This is also important given the longevity of the record and the lack of anthropogenic acfivity to provide alternafive drivers to DOC release dynamics.This finding will be of interest to a broad research audience, thus lending the paper impact and significance.The methods used throughout are sound.
However, I have concerns about the way the paper is presented, the sweeping interpretafions derived from the trace elements presented, the seemingly contradictory nature of some of the records, and in some cases the lack of aftenfion paid to exisfing research in the field.Each of these issues are explained further below.
1.The paper is presented on the understanding not only is there a temperature control on aqueous DOC dynamics, but there is also a rainfall control that can be clearly deciphered.However, this quickly begins to unravel as soon as the reader accesses the results secfion.I would suggest a minor re-structuring to redress these expectafions for the reader.
2. The issue above is compounded through the sweeping use of Mg/Ca as a rainfall proxy with liftle considerafion of the many alternafive explanafions that can be aftributed to changing Mg/Ca in the speleothem record.The assumpfion seems to be (although the explanafion for the reader is extremely poor), that prior calcite precipitafion will alter the rafio of Mg to Ca, such that drier condifions raise the concentrafion of Mg relafive to Ca.However, Mg/Ca rafios are impacted by many other factors.In the epikarst, concentrafions of magnesium can be driven by incongruent dissolufion, variable bedrock contact fime (including contact with variable proporfions of host dolomite), changing hydrological pathway, in addifion to prior calcite precipitafion.Within the cave, parfifioning across the drip watercalcite interface can alter speleothem Mg concentrafions via temperature, PCO2, crystal fabric, and growth rate.Thus, interpretafion of the Mg/Ca is often speleothem specific (let alone cave specific) and requires the support from other proxies to decipher the true nature of the Mg signal.This should include a thorough assessment of speleothem calcite 18O, Sr concentrafion dynamics, co-variafion between Mg and Sr, and other indicators (eg.Ba to eliminate growth rate effects) to thoroughly address the proxy signal interpreted from Mg/Ca in these two speleothems.There is plenty of literature available which addresses these drivers and compefing effects.Unfortunately, these assumpfions undermine all of the discussion regarding the effects of effecfive rainfall.It is thus liftle wonder that the data are difficult to interpret and seemingly compefing effects between Mg/Ca and DOC are seen.
3. The discussion surrounding some of the records is also a bit contradictory.There is confusion in the discussion of stage 2 regarding whether Dave's cave had higher, or lower, concentrafions of DOC than the preceding stage.This is purely confusion in wrifing style and needs to be cleaned up.Further, as it is apparent the two speleothem records have two opposite trends between DOC and rainfall this does not make for a convincing conclusion regarding rainfall as a driver of DOC dynamics.Whilst I appreciate rainfall drivers of DOC are complex, the reader is not informed about this unfil later in the discussion.This leads to confusion and lack of confidence in the way the data has been interpreted.I suspect the use of Mg as a rainfall indicator has also led to much of this poor interpretafion.It is also poor that drying trends (which incidentally are opposite to that expected) are idenfified post 6ka in the speleothem from Dave's cave, but most of this fime period is covered by a hiatus (Supplementary informafion, Figure 6).Despite this invoked drying trend, the subsequent sentences then proceed to idenfify the hiatus as due to undersaturafion of the drip waters in a climafically wet period.Confusing as currently wriften.Throughout, many of the corelafions idenfified between records require stafisfical tests to prove these.
4. I also felt as though there were many pieces of literature which were extremely relevant to the current manuscript, but which had not been paid aftenfion.These include the many ground breaking studies by Overall, I felt as though this was a manuscript that promised much and could have been so good!The lack of integrity with proxy interpretafion spoiled the key findings.There is much data interpretafion sfill to do before the story can be presented for publicafion in a journal such as Nature Communicafions.I hope these comments help a bit and I hope that the science comes to fruifion as it will be an excifing science story when it has been cleaned up and presented in a more thorough fashion.
Please see a point-by-point response to reviewers' comments (blue) which directly follow each referee comment (black).Relevant text pasted from the manuscript is in grey italics.

Reviewer 1:
Reviewer 1, comment #1: The DOC concentrafion proxy from speleothems and lake records has been developed and calibrated in previous studies, parficularly Pearson et al., 2020.I commend the authors for their terrific work with the proxy development and validafion.However, I would like to see some more crifical assessment of the uncertainfies that affect the DOC proxy.For example, while the humic-like fluorescence component can be separated from other components such as proteinlike, and therefore the soil-derived signal can be isolated from e.g., microbial components, I assume there is no way to isolate a signature that could come from soil-derived OM previously exported at depths below the soil?If such a component of OM existed and was periodically exported as DOC, could it lead to an over-esfimafion of the soil DOC export at these fimes?
Response: We wish to thank the reviewer for their comments on our previous work.We were concerned that there may be potenfial for over-esfimates of DOC owing to the processes described by the reviewer.Unfortunately, we do not have a method for separafing freshly exported soil DOC from material previously exported below the soil zone.
Although our previous research demonstrated that calcite can reliably record humic-like DOC concentrafions and characterisfics in a lab sefting, we were uncertain as to whether flowstones could be used to reconstruct DOC export in an environmental sefting (e.g., owing to complexifies regarding OM transport such as previously exported soil-derived OM present at depths below the soil and periodically exported from the vadose zone to the cave, or microbial degradafion of DOC within the cave itself).Thus, we decided to compare one of our flowstone archives (Hodge Creek Cave) against a proximal lake sediment archive (lake sediments are a more convenfional archive of OC).The relafive similarifies between the lake sediment and flowstone records give us confidence that (despite different DOC transport pathways), our results are robust, although we acknowledge the potenfial for error associated with the processes outlined by the reviewer.In essence, we consider that on the decadal-to-centennial resolufion represented by our datasets, stochasfic changes in DOC transport and storage within the epikarst and vadose zone would have been integrated by the speleothems and therefore were not an important part of the signal we observe in these records.We agree with the reviewer that it is important to highlight these uncertainfies, and have added a new subsecfion of the discussion fitled 'Limitafions' which includes the following text to highlight the need for further research on the contribufion of soil OM previously exported to depths below the soil profile:

"Further research should focus on paired analysis of soil DOC (ideally through soil profiles, as soil responses to climate change can be different through a profile) and dripwater-DOC. Paired analysis of soil vs cave DOC would provide insights on preferenfial removal or microbial transformafions of different DOC fracfions between soil and cave. For example, more hydrophobic fracfions of DOC are
likely to be preferenfially removed (owing to adsorpfion to mineral surfaces) in the vadose zone, meaning that hydrophilic DOC may be more prominent in cave environments 110 .Similarly, in most karst environments, overlying soil is likely to be the main source of DOC to a cave 40 .However, there are some uncertainfies in our assumpfion that humic-like DOC represents soil DOC.For example, soil-derived DOC could have previously been exported and stored in the vadose zone and then periodically mobilised into the cave (e.g., via hydrological or geochemical processes such as desorpfion from mineral surfaces), potenfially leading to over-esfimafions of soil DOC export at those fime intervals.Further, there are other potenfial sources of humic-like DOC (e.g., vegetafion and vadose zone sediments, biofilms) which may have contributed to the DOC pool measured at the cave sites".I really would welcome a more nuanced discussion of this proxy and the reliability of the results (parficularly in terms of quanfitafive reconstrucfion) in the paper, since as it stands it seems overconfident and potenfially misleading.

Response:
We propose that most humic-like OM present in the flowstones derives from overlying soils (including vegetafion and lifter which contributes to the SOC pool), given the presence of organic-rich soils overlying both caves (see Supplementary for images and descripfions of the soil profile).Nevertheless, we acknowledge that this is an assumpfion, and that there are other potenfial sources (e.g., vadose zone biofilms, DOC previously released and stored below the soil profile).We have proposed some future research on paired analysis of soil vs cave DOC (see response to previous quesfion) and have highlighted these uncertainfies and limitafions in the discussion secfion: "Although we measured humic-like DOC present in dripwaters and speleothems, the rate and extent to which DOC is processed and filtered during transport from soil to cave is poorly constrained 40 .Changes in DOC properfies may be explained by the soil confinuum model 12 , whereby organic mafter (including SOC) is considered as 'a confinuum of degrading compounds' ranging from intact plant material to highly oxidised carbon in carboxylic acids 12 .In the context of speleothem science, DOC properfies can be altered by microbial degradafion during transport from soil to cave 40 .In addifion, although DOC concentrafions are reliably recorded in the crystal laftice during precipitafion as shown in laboratory studies 39 , the effects of dynamic environmental condifions within a cave sefting (e.g., pH, redox state, venfilafion, microbial acfivity) are uncertain.Although we assessed the fluorescence intensity of the protein-like fracfion present in the flowstone cores, the extent to which microbial acfivity degraded DOC during transport and prior to calcite incorporafion is unclear.Notably, a protein-like fluorescence signal (indicafing microbial acfivity) was observed at Hodge Creek Cave, yet at Dave's Cave, a cooler cave at greater elevafion, no protein-like fluorescence was observed, with the fluorescence signal dominated by humic-like DOC".
Reviewer 1, comment #3: The interpretafion of speleothem Mg/Ca as a tracer for effecfive precipitafion is not well backed up by data or further references.While Mg/Ca can be a tracer for effecfive infiltrafion, it can also relate to other processes, such as water-rock interacfion (variability in the host rock composifion).Is there monitoring data from the two caves that can help determining if this is the case?Data from the host rock?Replicafion with other speleothems?In any case, the authors need to provide more background informafion on how the interpretafion of Mg/Ca was derived.It would also be nice to see a comparison with modelling data, as a check whether their hydroclimafic interpretafion reflects modelled condifions (check Scheff et al., 2017, Journal of Climate for a nice example).

Response:
We thank the reviewer for this helpful comment.We agree that our previous submission lacked several important references, and we acknowledge that we did not provide enough detail on how the interpretafion of Mg/Ca was derived.We added the following text and Figure 2 into our 'Results and Discussion':

"Inorganic and prior calcite precipitafion proxies in dripwaters and flowstones
Given the relafive dearth of paleo-hydrologic data from Aotearoa, we developed a mulfi-proxy dataset based on speleothem prior calcite precipitafion (PCP) proxies 58,59 , which are increasingly applied in speleothem paleoclimate studies to indicate hydrologic change, in addifion to more convenfional oxygen ( 18 O) and carbon ( 13 C) isotope rafios.PCP proxies respond to the precipitafion of calcite along the speleothem flowpath and broadly reflect drier, befter-venfilated condifions within the epikarst, karst aquifer, and cave environment.In some speleothems, Mg/Ca and Sr/Ca provide insight on effecfive infiltrafion (and therefore effecfive rainfall) through PCP and other controls, which increase Mg/Ca and Sr/Ca rafios during drier periods 70 .However, results can be confounded by local hydrological controls on water evolufion and flow paths 71 .Calcium isotope rafios (δ 44/42 Ca) have emerged as a proxy for local infiltrafion 72,73 , as the lighter isotope ( 42 Ca) is preferenfially precipitated during PCP 72,74 .Factors controlling oxygen isotopes (δ 18 O) are numerous and complex 75 , including sensifivity to cave temperature and effecfive precipitafion (amount, or moisture source) 76,69 , however more posifive values may indicate lower rainfall when the amount effect is acfive.δ 13 C behaviour in cave systems is also highly complex 77 , and can be influenced by soil respirafion 78 , and in-cave processes such as drip rate and degassing 79 .δ 13 C variability in high-alfitude speleothems has also been aftributed to changes in vegetafion cover and/or soil thickness 80 , including in Mount Arthur flowstones (Figure 3) 65 .However, δ 13 C can also move posifively due to PCP, and covariafion with Mg/Ca can suggest PCP influence.Addifionally, covariance between δ 13 C and δ 18 O may represent increased kinefic fracfionafion, another indicator of relafively dry condifions in the epikarst.

PCP proxies respond to drier condifions because aridity increases the potenfial for gas exchange along dripwater flow paths. While PCP proxies have been interpreted within quanfitafive frameworks
elsewhere 59 , a fully quanfitafive treatment requires empirical funcfions between moisture balance and PCP, and further necessitates long-term monitoring datasets that are beyond the scope of this study.However, atomic rafios of magnesium (Mg) and stronfium (Sr) to calcium (Ca) in modern dripwater samples, both Mg/Ca and Sr/Ca in Hodge Creek Cave and Dave's Cave largely cohere with expected evolufions due to PCP (Figure 2a) 81   all data shown in the fimeseries in Figure 3. Solid lines reflect respecfive linear best fits.For both speleothems, the slopes of this relafionship cohere with a dominant hydrological control due to PCP.
To buftress our interpretafions from trace element records from Hodge Creek Cave, we include published oxygen (δ 18 O) and carbon (δ 13 C) isotope records from Exhaleair Cave and Neftlebed Cave 65,66 , which (like Hodge Creek Cave) are posifioned on Mount Arthur, albeit at lower elevafions (685 m and 390 m a.s.l., respecfively).From the Dave's Cave flowstone, we present Mg/Ca and Sr/Ca alongside δ 44 Ca, δ 18 O, and δ 13 C (Figure 3).Allowing for these caveats, the hydrological proxy data at large show

Response:
The results shown are based off one laser ablafion track for each sample.However, to support our interpretafion of Mg/Ca, we have now included Sr/Ca records from flowstones at both Hodge Creek and Dave's Cave.To buftress our interpretafions from our trace element records at Hodge Creek Cave, we also show previously published stable oxygen and carbon isotope records from Exhaleair Cave and Neftlebed Cave 1,2 , which (like Hodge Creek Cave), are posifioned on Mount Arthur, albeit at lower elevafions (685 m and 390 m a.s.l., respecfively).From Dave's Cave, we show reconstrucfions of Mg/Ca and Sr/Ca alongside stable records of oxygen, carbon, and calcium isotopes, the lafter providing the most direct measure of PCP among these proxies.
Unfortunately, there may have been a misunderstanding regarding our descripfion of seasonality.
The fime-resolufion for our speleothem and lake sediment records is too coarse for any analysis of seasonal (or even annual) signals, however we cite previously published research to suggest that changes in seasonality (e.g., higher mean annual temperature with cooler summers and warmer winters) could have impacted long-term soil DOC export.For example, McGlone et al., 2011     proposed that the HCO may have had 'reduced seasonality' (i.e., cooler summers and warmer winters) 3,4 (e.g., due to increased net primary producfivity, forest expansion and treeline elevafion owing to longer growth seasons).Thus, we suggest that that reduced seasonality 3,5,6 through the HCO may have contributed to ecosystem change (producfion and/or degradafion of SOC) which led to increased DOC increased export, most notably during the HCO.We have pasted some relevant text from our results and discussion secfion: "The Holocene Climafic Opfimum (HCO, ~12.5-9 kyrs) was ~1-2.5°Cwarmer than the immediate preindustrial period 31,83,84 with at least 30% lower precipitafion across most of Aotearoa Exhaleair and Neftlebed Caves 65 .Drier condifions are also consistent with a lake sediment reconstrucfion from southern New Zealand, whereby periods of extended low lake levels (from 10-8 kyrs) were aftributed to diminished wind strength, higher air temperatures (as evidenced by increased biogenic silica), and reduced seasonality 88 ".

And:
"Despite higher mean annual temperatures, the plant macrofossil record from Adelaide Tarn suggests a lower-than-modern treeline through most of this period, wherein catchment vegetafion was exclusively dominated by graminoids and bryophytes 31,62 .Based on palynological evidence from Adelaide Tarn, Jara et al. (2015) proposed that forest communifies expanded upslope as a response to sustained warming from ~12.5 ka onwards, however, tree macrofossils first appear in the Adelaide Tarn core towards the end of the HCO at 9.7 ka 62 , providing unequivocal evidence for the relafively late arrival fime of trees in the catchment.The slow migrafion of trees into the catchment was aftributed to high relief and rugged topography 62 , or (despite warmer mean annual temperatures) cooler summers and warmer winters (which can restrict treeline elevafion, as reconstructed elsewhere on Te Waipounamu/South Island), a warmer ocean, and reduced westerly wind flow 62,83 ".
Reviewer 1, comment #5: In general, the interpretafion often lacks specificity and the data to back up some of the claims appears insufficient.Some of the claims seem cherry picked, and often are based on 1-2 data points given the resolufion of the records.I tried poinfing them out in the list of line-by-line comments below.Again, toning down the language in the manuscript, providing more details as to what could be potenfial complexifies or issues in the dataset, would lead to a much more interesfing and robust paper.

Response:
We thank the reviewer for this comment and have edited and added text to our manuscript to reflect the nuances, complexifies, and limitafions of our findings, and have toned down our language.
However, we respecffully contest the asserfion that some of the claims are based on one or two data points (e.g., relafively elevated DOC concentrafions during the HCO are evident in both Hodge Creek Cave, Adelaide Tarn, and Dave's Cave).We agree that our figures did not clearly show our data points, and have amended Figure 4  It's also difficult to relate the z-score here to the absolute numbers described in the text.I would like to see a second version of the figure with absolute values.

Response:
We have now changed the figure to be clearer.To avoid repefifion, we chose to amend our figures to show absolute values instead of z-scores for both Figures 3 and 4. For visual clarity, we have also plofted data for each proxy separately.
Reviewer 1, comment #8: Line 188 and following: I find the separafion of the three periods a bit confusing.Here, the peak described seems to already be in stage 2 at about 12ka? (Difficult to be sure because of the axis being in z-score and text in absolute numbers).Either way, it seems to me that the Hodge creek cave record also mainly oscillates.There is a very high DOC value at 12 ka, but then values decrease again to levels comparable to the glacial and close to the mean of today.So the wording here is misleading.

Figure 2 :
Figure 2: The different trends and shapes of the records are difficult to see in this figure.I would suggest at least to plot the "climate" records (precip and T) separately form DOC. It's also difficult to relate the z-score here to the absolute numbers described in the text.I would like to see a second version of the figure with absolute values.

Finally, would the
authors consider adding mulfi-proxy data to support their new fluorescence proxy.Further LA-ICP-MS analyses of metal-transported trace elements, for example, would help understand the nature of the DOC being transported to the cave.Analysis of flowstone colour would be another proxy, I think one proposed previously by Pearson et al. (2020)?If colour calibrates with the fluorescence proxy, could it also enable a high-resolufion record to be derived in a similar way that the authors use FTIR for the lake proxy record.Retallack Gregory J. (2021) Soil, Soil Processes, and Paleosols.In: Alderton, David; Elias, Scoft A. (eds.)Encyclopedia of Geology, 2nd edifion.vol.2, pp.690-707.United Kingdom: Academic Press.x.doi.org/10.1016/B978-0-12-409548-9.12537-0 Reviewer #3 (Remarks to the Author): Review comments for: NCOMMS-23-30654-T Warming increases dissolved organic carbon export from prisfine Alpine soils.
Baker et al. who pioneered the use of fluorescence EEM's to infer organic content of speleothem calcite; the more recent work by Blyth et al pioneering the extracfion and molecular analysis of organic compounds from speleothem calcite, and the issues of contaminant molecules raised by Wynn and Brocks, 2014.(Rapid Communicafions in mass spectrometry).The work by Webb et al. 2014 (Journal of Quaternary Science) that addresses DOC in speleothem calcite from Australia and links this to the different proxy indicators of pluvial and arid phases; the wealth of literature surrounding interpretafion of Mg and Sr in the speleothem record as indicators (or not) of prior calcite precipitafion (Fairchild, numerous references; Sinclair et al., 2012.Chemical Geology) should also be addressed.There is also very liftle reference to the work of Worral et al in the opening stages of the manuscript, paying reference to the work they have undertaken highlighfing changing DOC fluxes from peatlands over the monitoring period.

Reviewer 1, comment # 2 :
What about the general uncertainfies with the interpretafion of fluorescence signals and the calibrafion to DOC amounts?What about uncertainty in the meaning of the humic-like component (i.e., does it always have to relate to soil OM or are there other potenfial sources?).
. In the flowstone records, this imprint of PCP is supported by the slopes of Mg/Ca versus Sr/Ca signatures (in natural logarithm space; Figure 2b) of ca.0.64 and 0.81 for Hodge Creek and Dave's Cave, respecfively 71 .Although addifional processes (e.g., incongruent calcite dissolufion) likely contribute to Mg and Sr signatures (parficularly in Dave's Cave), these data support the interpretafion of karst hydrology as the dominant control.

Figure 2 -
Figure 2-a) Atomic rafios of Mg and Sr to Ca in dripwater samples from Hodge Creek Cave (blue dots) and Dave's Cave (red dots).Solid coloured lines reflect respecfive linear fits.Dofted coloured lines indicate theorefical relafionships between Mg/Ca and Sr/Ca as a funcfion of PCP for each cave, calculated for a limestone bedrock with small contribufions of Mg from dolomite 81 ; see Methods for details).b) Flowstone Mg/Ca and Sr/Ca signatures (expressed as natural logarithms), including coherent trends and allow qualitafive interpretafions with which to test the controls on DOC variafions presented in Figure 4. Evolufion of hydrological changes are discussed in relafion to DOC dynamics in the remainder of the text."Reviewer 1, comment #4: Moreover, it is unclear to me whether the results shown are based off one single laser ablafion track?This could also lead to strong skewing of the results, based on lateral variability of Mg/Ca in the stalagmite.Without long-term monitoring and more detailed analysis of the flowstones (e.g., more than one LA sampling track) this is a rather tenuous interpretafion.In that case, the claim that warming is the dominant driver of DOC export from these soils, and not hydroclimate, would not be backed up by the data.Similarly, the interpretafion of possible seasonality signals in the data seems mostly based off speculafion.A clearer descripfion of how the data was generated and what gives the authors confidence that this proxy reflects effecfive precipitafion at both cave sites is needed, including reflecfion on what potenfial sources of uncertainty could be, and how they would affect the results.
so that individual data points are shown (rather than lines as shown previously) (see Figure 4 in manuscript).Reviewer 1, comment #6: Line 145: fragment sentence "Hodge Creek Cave (41° S, 172° E) is located ~32 ..." Response: Thank you-this is now changed.Reviewer 1, comment #7: Figure 2: The different trends and shapes of the records are difficult to see in this figure.I would suggest at least to plot the "climate" records (precip and T) separately form DOC.
53,56.Numerous palaeoenvironmental reconstrucfions indicate higher mean annual temperatures than present; however, lower treelines (including at Adelaide Tarn) indicate reduced seasonality (i.e., cooler summers and warmer winters) 85,86 , possibly associated with lower summer insolafion intensity 87 and weaker westerlies in the Aotearoa sector of the Southern Ocean 54 .These condifions likely led to reduced orographic rainfall and ulfimately drier condifions across northern Te Waipounamu/South Island.At Hodge Creek Cave, elevated Mg/Ca, Sr/Ca and may indicate relafively drier condifions, an interpretafion supported by more posifive δ 18 O rafios (weaker amount effect) in flowstones from both